An everting catheter is commonly used to gain access to various regions of the human body. With the catheter properly placed, an instrument, such as an endoscope or other elongated member can be passed through the lumen of the catheter to carry a desired function adjacent the distal end of the catheter.
An everting catheter typically includes an elongated catheter body having a lumen with a distal opening, an elongated inner tube having a flexible distal end portion and a flexible everting element coupled to the catheter body and to the inner tube. With this construction, the everting element can be inverted and everted through the distal opening. The inner tube, which may be considered as an inner catheter, has an inner tube lumen extending through the distal end portion of the inner tube. With the catheter properly positioned within a patient, an endoscope or other instrument is advanced through the inner tube lumen to the desired body region. Alternatively or in addition thereto, a fluid, such as a drug, can be infused through the inner tube lumen or the inner tube lumen may be used for aspiration.
To enable the distal end portion of the inner tube to conform to curved or tortuous body passages, it is important that the distal end portion of the inner tube be flexible. On the other hand, the distal end portion of the inner tube cannot be so flexible that it collapses radially inwardly to occlude or partially occlude the inner tube lumen because this lumen must remain open for the passage of a medical instrument or for infusion or aspiration purposes. For example, if the distal end portion of the inner tube is not sufficiently resistant to radial compressive forces, it may collapse, or partially collapse, due to various factors, such as the internal fluid pressure within the everting element or it may kink in navigating a curve within the body. Unfortunately, the requirements for flexibility and rigidity against radial compressive loads are inconsistent, and the prior art techniques of which we are aware have not satisfactorily achieved both flexibility and resistance to radial inward loads.
Another problem with everting catheters is that retraction or proximal movement of the inner tube too far may damage or even rupture the thin, flexible everting element. When this occurs, the catheter is effectively rendered useless for its intended purposes and cannot be safely used.